Summary.This paper challenges the current consensual view that classical urbanism continued in Britain to the end of the Roman period. It offers a quantitative analysis of structures, deposits and artefacts at Roman Colchester, and discusses a number of interpretative problems arising from this material. It is argued on the basis of this evidence that a profound change occurred in the character of the town between c.250 andc. 325, and that this constituted the end of classical urbanism on the site and the emergence of a distinctively late Roman urban settlement – a ‘post‐classical’ town. A description of the principal characteristics of fourth century Colchester as known from archaeology is offered, and an attempt is made to put this in the context of the third century crisis and the late Roman rev